A coordinate system, which uses the distance from the coordinate system center and positional angles to identify points in space rather than orthogonal independent unit vectors as in the Cartesian coordinate system. Polar and partly polar (cylindrical) coordinate systems are widely used to describe spin motion in NMR experiments.
It is important to know how to compute the coordinates of a point in the polar coordinate system when they are given in a Cartesian system and vice versa. The length of the vector r pointing from the coordinate origin to a point in 2D space is given as
r = √(x² + y²).
while the polar or phase angle f is obtained by performing the operation
f = arctan (y/x),
where the arctan function is the inverse of the tangent function.

High permeability material used to shape the uniformity of the useful volume of a magnet, especially a permanent magnet. Also called Pole Tip.

From Odin Medical Technologies, Inc.;
the PoleStar™ N-10 is a compact, mobile MRI scanner that mounts to a standard operating room table. The magnets raise into position for imaging, but lower to make surgery easier, and the low magnetic field makes it possible to use many conventional surgical instruments.
When not in use, the PoleStar™ is stored in a nearby closet that allows the room to be used for conventional surgical procedures. The PoleStar™ N-10 is supplied with a fully integrated image guidance system that utilizes intraoperatively acquired images.
The successor, the new PoleStar™ N20 sets a new standard in intraoperative magnetic resonance imaging.

Short name: PION, generic name: Polycrystalline iron oxide nanoparticles, central moiety: Fe2+/Fe3+, relaxivity: T2*enhanced, r2//r1=4.4, r2//r1=7
A substance under development (preclin.) as an RES-directed MRI contrast agent (larger particles = DDM 128, PION-ASF) for MR lymphography and the detection of liver lesions.

The numbers of nuclei or electrons in different energy levels. At thermal equilibrium, the relative populations of the energy levels will be given by the Boltzmann distribution.

See also Boltzmann Distribution.